Optical recording medium and method of manufacturing same

ABSTRACT

An optical recording medium includes a first recording member having a first light-transmissive substrate and a first semi-light-transmissive information area disposed on a surface of the first light-transmissive substrate, and a second recording member having a second substrate and a second reflective information area disposed on a surface of the second substrate. The first recording member and the second recording member are joined to each other with the transparent layer interposed therebetween with the first and second information areas facing each other.

This application is a divisional of application Ser. No. 08/605,362filed Feb. 22, 1996, now U.S. Pat. No. 6,111,851.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical recording medium and amethod of manufacturing such an optical recording medium.

2. Description of the Related Art

There have been known optical recording mediums such as optical disks,cards, etc. for recording and/or information such as audio information,video information, etc. with the application of light. It has beenproposed to increase the amount of information that can be recorded onan optical recording medium by employing an information recordingsurface thereof which is of a multilayer structure.

One such proposal is illustrated in FIG. 1 of the accompanying drawings.As shown in FIG. 1, an optical disk has a pair of first and secondrecording members 1, 2 which comprises respective transparent substrates1S, 2S, respective information areas 1M, 2M disposed on respectivesurfaces of the transparent substrates 1S, 2S and carrying recordedinformation in the form of information pits, and respective reflectingsurfaces 1R, 2R of evaporated aluminum, for example, disposedrespectively on the information areas 1M, 2M. The first and secondrecording members 1, 2 are bonded to each other by an adhesive 3 withthe information areas 1M, 2M facing each other.

For reading or reproducing recorded information from the informationareas 1M, 2M, reading light (hereinafter referred to as reproducinglight) 1L is applied to the information area 1M through the transparentsubstrate 1S, and reproducing light 2L is applied to the informationarea 2M through the transparent substrate 2S. Therefore, a drive unitfor use with the optical disk has a double optical pickup structureincluding two playback optical pickups positioned in confrontingrelationship to the opposite surfaces of the optical recording mediumfor applying reproducing light to the respective information areas 1M,2M, or alternatively, a single optical pickup for applying reproducinglight to the information areas 1M, 2M which have selectively beenbrought into facing relationship to the optical pickup by reversing theoptical disk.

The drive unit of the double optical pickup structure is large in size,made up of a large number of parts, and heavy in weight. The drive unitwith the single optical pickup needs a complex mechanism forautomatically reversing the optical disk in order to successivelyreproduce recorded information from the information areas 1M, 2M.Therefore, the drive unit with the single optical pickup is also largein size, made up of a large number of parts, and heavy in weight.

To avoid the above difficulties, there has been proposed an opticalrecording medium capable of reproducing information recorded ontwo-layered information recording areas with light applied from one sideof the optical recording medium. The optical recording medium and amethod of manufacturing same will be described below with reference toFIGS. 2A through 2D of the accompanying drawings.

As shown in FIG. 2A, a first transparent substrate 21S isinjection-molded of polycarbonate (hereinafter referred to as “PC”)which has a first information area 21M comprising information pitsrepresentative of recorded information. Then, as shown in FIG. 2B, asemitransparent optical layer 23, for example, a sputtered layer of SiN,is formed on the first information area 21M for controlling thetransmittance and reflectance in the first information area 1M atdesired values. Thereafter, a second information area is formed of anultraviolet-curing resin on the semitransparent optical layer 23 by aphotopolymerization process, e.g., a so-called 2P process. Morespecifically, as shown in FIG. 2C, a stamper 25 having a pattern ofconvex and concave shapes for forming a second information area ispressed against the semitransparent optical layer 23 through anultraviolet-curing resin 24, and then the ultraviolet-curing resin 24 iscured by an ultraviolet radiation applied from the side of the firsttransparent substrate 21S. Thereafter, as shown in FIG. 2D, the stamper25 is removed, leaving a second information area 22M, transferred fromthe pattern of convex and concave shapes of the stamper 25, on theultraviolet-curing resin 24. A reflecting film 26 of evaporated aluminumor the like is deposited on the second information area 22M, and thencovered with a protective layer 27 of a photosetting resin or the like.In this manner, the optical recording medium with the first and secondinformation areas 21M, 22M is manufactured.

For reproducing information recorded on the optical recording mediumwith light, the light is applied to the optical recording medium fromthe side of the transparent substrate 21S. More specifically, as shownin FIG. 2D, to reproduce recorded information from the first informationarea 21M, reproducing light 21L which is focused on the firstinformation area 21M is applied from the side of the transparentsubstrate 21S, and light reflected by the first information area 21M isdetected to read the information. To reproduce recorded information fromthe second information area 22M, reproducing light 22L which is focusedon the second information area 22M is applied from the side of thetransparent substrate 21S, and light reflected by the second informationarea 22M is detected to read the information.

Since the information recorded on the first and second information areas21M, 22M can be reproduced with light applied from one side, a driveunit for use with the optical-recording medium may have a single opticalpickup. As the optical recording medium does not need to be reversed,the drive unit may be small in size, light in weight, simple instructure, and easy to assemble. However, because the information area22M is formed by the 2P process, the optical recording medium isrequired to be formed in layers, and cannot be mass-producedefficiently.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an opticalrecording medium which allows information to be reproduced from and/orrecorded on a plurality of layered information areas with light appliedfrom one side of the optical recording medium, permits a drive unit forthe optical recording medium to have a single optical pickup without theneed for reversal of the optical recording medium, and can bemass-produced highly efficiently.

According to the present invention, there is provided an opticalrecording medium comprising a first recording member having a firstlight-transmissive substrate and a first semi-light-transmissiveinformation area disposed on a surface of the first light-transmissivesubstrate, a second recording member having a second substrate and asecond reflective information area disposed on a surface of the secondsubstrate, and a transparent layer, the first recording member and thesecond recording member being joined to each other with the transparentlayer interposed therebetween with the first and second informationareas facing each other.

According to the present invention, there is also provided a method ofmanufacturing an optical recording medium, comprising the steps ofseparately fabricating a first recording member having a firstlight-transmissive substrate and a first semi-light-transmissiveinformation area disposed on a surface of the first light-transmissivesubstrate, and a second recording member having a second substrate and asecond reflective information area disposed on a surface of the secondsubstrate, and joining the first recording member and the secondrecording member to each other with a transparent layer interposedtherebetween with the first and second information areas facing eachother.

The terms “light-transmissive”, “semi-light-transmissive”, “reflective”,and “transparent” used herein are intended to signify the propertiescapable of transmitting, partly transmitting, reflecting, and passinglight that is applied to optically reproduce information from and recordinformation on the optical recording medium.

With the arrangement of the present invention, the first recordingmember with the first information area and the second recording memberwith the second information area are fabricated separately from eachother and then joined to each other, resulting in a laminated structureof the first and second information areas. Since the first informationarea is semi-light-transmissive and the second information area isreflective, information can be recorded on and/or reproduced from thefirst and second information areas with light which is applied from theside of the first information area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional optical recordingmedium;

FIGS. 2A through 2D are cross-sectional views showing a process ofmanufacturing the conventional optical recording medium;

FIG. 3 is a cross-sectional view of an optical recording mediumaccording to the present invention;

FIG. 4 is a cross-sectional view of a first recording member of theoptical recording medium according to the present invention;

FIG. 5 is a cross-sectional view of a second recording member of theoptical recording medium according to the present invention;

FIGS. 6A and 6B are diagrams illustrative of directions in whichrecording progresses on respective information areas of the opticalrecording medium according to the present invention; and

FIG. 7 is a cross-sectional view of an injection-molding mold used in aprocess of manufacturing the optical recording medium according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The principles of the present invention are applied to an opticalrecording medium such as an optical disk, a card, etc. for recordingand/or reproducing information such as audio information, videoinformation, etc. with the application of light.

FIG. 3 shows in cross section an optical disk, to which the presentinvention is applied, of the ROM(read-only memory)-type havinginformation areas comprising pits in a pattern of convex and concaveshapes representative of information that can be read by the applicationof light thereto.

The optical recording medium or disk according to the present inventioncomprises a first recording member 31 having a first light-transmissivesubstrate 31S which supports on one surface thereof a firstsemi-light-transmissive information area 31M, as shown in FIG. 4, and asecond recording member 32 having a second substrate 32S which supportson one surface thereof a second reflective information area 32M, asshown in FIG. 5. The first and second members 31, 32 are joined to eachother by a transparent layer 33 with the first and second informationareas 31M, 32M confronting each other.

Reproducing light 31L, 32L for reading information recorded by pits onthe first and second information areas 31M, 32M as shown in FIG. 3 isapplied to the optical recording medium or disk from a surface of thefirst recording member 31 opposite to the first information area 31M,i.e., a back surface of the first recording member 31.

The first information area 31M, which is semi-light-transmissive, has areflectance ranging from 20% to 50% and a transmittance ranging from 30%to 80%.

The second information area 32M, which is reflective, has a reflectanceof 60% or more.

The first and second information areas 31M, 32M have respectiverecording tracks 31T, 32T (see FIGS. 6A, 6B) arranged coaxially witheach other. As shown in FIGS. 6A and 6B, recording progresses in thefirst and second information areas 31M, 32M, as they rotate, in the samedirection indicated by the arrows as viewed from the side from which thereproducing light is applied.

As shown in FIG. 6A, the recording track 31T of the first informationarea 31M extends progressively radially outwardly along the direction inwhich recording progresses as indicated by the arrow. As shown in FIG.6B, the recording track 32T of the second information area 32M extendsprogressively radially inwardly along the direction in which recordingprogresses as indicated by the arrow.

The optical recording medium or disk according to the present inventionis manufactured as follows: The first recording member 31 with the firstlight-transmissive substrate 31S supporting on one surface thereof thefirst semi-light-transmissive information area 31M, as shown in FIG. 4,and the second recording member 32 with the second substrate 32Ssupporting on one surface thereof the second reflective information area32M, as shown in FIG. 5, are fabricated separately from each other.

If the information areas 31M, 32M comprise pits representing recordedinformation, as shown in FIG. 3, then the first and second recordingmembers 31, 32 are injection-molded of a transparent resin such as PC orthe like by a mold 40 (see FIG. 7). For injection-molding the firstrecording member 31, a master stamper 41 having a pattern of convex andconcave shapes for forming the first information area 31M is placed inthe cavity of the mold 40, and a transparent resin such as PC, forexample, in a molten state is injected into the cavity. Forinjection-molding the first recording member 31, a master stamper 42having a pattern of convex and concave shapes for forming the secondinformation area 32M is placed in the cavity of the mold 40, and atransparent resin such as PC, for example, in a molten state is injectedinto the cavity.

The pattern of convex and concave shapes on one of the master stampers41, 42 represents information recorded successively radially outwardlyfrom its center in either a clockwise or counterclockwise directionaround the center, and the pattern of convex and concave shapes on theother of the master stampers 41, 42 represents information recordedsuccessively radially inwardly toward its center in either acounterclockwise or clockwise direction around the center.

The master stampers 41, 42 may be fabricated in a known manner.Specifically, a glass substrate having a mirror surface, for example, iscoated with a photoresist, which is then exposed to a pattern image by alaser beam which has been modulated, e.g., turned on and off, withinformation to be recorded, while the laser beam is being rotatedrelatively to the glass substrate and moved radially relatively to theglass substrate to scan the same. Thereafter, the pattern image on thephotoresist is developed into a pattern of convex and concave shapes,which is then plated with a metal, such as silver, thereby forming adisk master. The disk master is plated with a metal such as nickel,forming a metal mask having a pattern of convex and concave shapes thatis a reversal of the pattern of convex and concave shapes on the diskmaster. The pattern of convex and concave shapes on the metal mask isthen plated with a metal such as nickel, forming a mother having apattern of convex and concave shapes that is a reversal of the patternof convex and concave shapes on the metal mask. The mother is similarlyplated, forming the master stampers 41, 42 having a pattern of convexand concave shapes that is a reversal of the pattern of convex andconcave shapes on the mother.

When the photoresist on the glass substrate for the formation of one ofthe master stampers 41, 42 is exposed to a pattern image by a laser beammodulated with information to be recorded, the laser beam is applied tothe photoresist successively radially outwardly from its center ineither a clockwise direction, for example, around the center. When thephotoresist on the glass substrate for the formation of the other of themaster stampers 41, 42 is exposed to a pattern image by a laser beammodulated with information to be recorded, the laser beam is applied tothe photoresist successively radially inwardly toward its center ineither a counterclockwise direction, for example, around the center.

Using the master stampers 41, 42 thus fabricated, the first transparentsubstrate 31 with the first information area 31M thereon and the secondtransparent substrate 32 with the second information area 32M thereonare injection-molded.

As shown in FIG. 4, a semitransparent film 34 of SiN, SiO₂, or the likeis deposited to a thickness of 150 Å on the first information area 31Mby evaporation, sputtering, or the like. The semitransparent film 34thus deposited makes the first information area 31Msemi-light-transmissive, having a reflectance ranging from 20% to 50%and a transmittance ranging from 30% to 80%, as described above.

As shown in FIG. 5, a film 35 of aluminum or the like is deposited to athickness of 500 Å on the second information area 32M by evaporation orthe like. The film 35 thus deposited makes the second information area32M reflective, having a reflectance of 60% or more, as described above.

The transparent substrates 31S, 32S are joined to each other by thetransparent layer 33 interposed therebetween with the first and secondinformation areas 31M, 32M confronting each other. The transparent layer33 may be made of a photosetting transparent resin, e.g., anultraviolet-curing transparent resin, which may be placed and pressedbetween the transparent substrates 31S, 32S and then cured by light,e.g., a ultraviolet radiation, applied from the side of the firsttransparent substrate 31S. The first transparent substrate 31S and thefirst information area 31M are transmissive or semi-transmissive withrespect to the ultraviolet radiation that is applied to cure theultraviolet-curing transparent resin.

The distance between the first and second information areas 31M, 32M isset to a desired value, such as 40 μm, for example, by the thickness ofthe transparent layer 33, such that it will not cause an interference inlight reflected by the first and second information areas 31M, 32M whenreproducing light is applied. The transparent substrates 31S, 32S, i.e.,the first and second recording members 31, 32, are now joined to eachother, thus producing the optical recording medium or disk.

With the optical recording medium or disk thus finally manufactured, therecording tracks 31T, 32T on the first and second information areas 31M,32M are arranged such that recording progresses along the recordingtracks 31T, 32T in the same direction as viewed from the side from whichthe reproducing light is applied, and the recording track 31T extendsprogressively radially outwardly along the direction in which recordingprogresses, whereas the recording track 32T extends progressivelyradially inwardly along the direction in which recording progresses.

The recording tracks 31T, 32T on the first and second information areas31M, 32M may be of a spiral shape or a concentric ring shape.

The transparent substrates 31S, 32S of the first and second recordingmembers 31, 32 have substantially the same thickness, e.g., of 1.2 mm or0.6 mm. This thickness is effective in preventing the optical recordingmedium, which is made up of the joined transparent substrates 31S, 32S,from being warped or otherwise deformed by a thermal expansion orcontraction due to the ambient temperature.

The arrangement of the present invention as described above offersvarious advantages given below. Since the optical recording medium is ofa multilayer structure including the first and second information areas31M, 32M superimposed on each other, the optical recording medium has anincreased information storage capability. Inasmuch as the firstinformation area 31M is semi-light-transmissive, it allows reproducinglight applied from the same side as reproducing light applied to thefirst information area 31M to reach the second information area 32Mthrough the first information area 31M, and also allows light reflectedfrom the second information area 32M to be detected through the firstinformation area 31M. Therefore, recorded information can be read basedon an interference due to information pits, for example, in the firstand second information areas 31M, 32M.

As described above, the first information area 31M has a reflectanceranging from 20% to 50% and a transmittance ranging from 30% to 80%, andthe second information area 32M has a reflectance of 60% or more. Thissubstantially equalizes the amount of reading light applied to the firstinformation area 31M to the amount of reading light applied to thesecond information area 32M. Accordingly, a circuit required foradjusting output powers of information reading light is simplified.

The recording tracks 31T, 32T of the first and second information areas31M, 32M are arranged coaxially with each other. As viewed from the sidefrom which the reproducing light is applied, recording progresses in thesame direction along the recording tracks 31T, 32T of the first andsecond information areas 31M, 32M. The recording track 31T of the firstinformation area 31M extends progressively radially outwardly along thedirection in which recording progresses as indicated by the arrow,whereas the recording track 32T of the second information area 32Mextends progressively radially inwardly along the direction in whichrecording progresses as indicated by the arrow. If each of the recordingtracks 31T, 32T is of a spiral shape, then information can be recordedand/or reproduced continuously along the recording tracks 31T, 32T.Therefore, the period of time for which information is continuouslyrecorded and/or reproduced can be increased.

In the above embodiment, the present invention has been described asbeing embodied in an optical disk in the form of a ROM with each of thefirst and second information areas 31M, 32M comprising information pitsin the form of convex and concave shapes. However, the information areas31M, 32M are not limited to the illustrated recording configuration. Thepresent invention may be applied to an optical recording medium whichallows information to be optically recorded, written once, andrewritten. The information areas 31M, 32M may be arranged such that theyallow information to be recorded and reproduced in the same mode as eachother or in different modes from each other. For example, theinformation areas 31M, 32M may be of a phase-change recordingarrangement for recording information through changes in opticalcharacteristics based on a phase change between amorphous andcrystalline states, or of a magnetooptical recording arrangement.

In the above embodiment, the optical recording medium is constructed ofthe first and second recording members 31M, 32M which are joined to eachother. However, the optical recording medium may be constructed of threeor more superimposed recording members.

The optical recording medium and the method of manufacturing sameaccording to the present invention are not limited the optical disk, butmay be directed to a card or the like. Therefore, the optical recordingmedium and the method of manufacturing same according to the presentinvention are not limited to the illustrated embodiment, but may bemodified in various ways.

The optical pickup used herein is not limited to a playback pickup, butshould be interpreted to include any device having an optical recordingcapability.

With the optical recording medium according to the present invention, asdescribed above, since information is recorded on and/or reproduced froma plurality of information areas with light applied from one side of theoptical recording medium, the optical recording medium can be used witha single optical pickup, resulting in a drive unit which is small insize, light in weight, and simple in structure.

Because the optical recording medium is constructed of independentlyfabricated first and second recording members that are joined to eachother, the optical recording medium can be mass-produced much moreeasily and efficiently than it would be manufactured by the 2P process.The first and second recording members that are joined to each othermake the optical recording medium highly mechanically strong. Forexample, the mechanical strength of the optical recording medium is highwhen each of the first and second recording members 31, 32 has athickness of 0.6 mm as well as 1.2 mm. Since the thickness of each ofthe first and second recording members 31, 32 may be either 0.6 mm or1.2 mm, the drive unit for use with the optical recording medium mayeasily be made compatible with disks with the 1.2-mm and 0.6-mmrecording members.

The recording tracks 31T, 32T of the first and second information areas31M, 32M are arranged coaxially with each other. As viewed from the sidefrom which the reproducing light is applied, recording progresses in thesame direction along the recording tracks 31T, 32T of the first andsecond information areas 31M, 32M. The recording track 31T of the firstinformation area 31M extends progressively radially outwardly along thedirection in which recording progresses as indicated by the arrow,whereas the recording track 32T of the second information area 32Mextends progressively radially inwardly along the direction in whichrecording progresses as indicated by the arrow. If each of the recordingtracks 31T, 32T is of a spiral shape, then information can be recordedand/or reproduced continuously along the recording tracks 31T, 32T.Therefore, the period of time for which information is continuouslyrecorded and/or reproduced can be increased.

Having described a preferred embodiment of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to that precise embodiment and that various changes andmodifications could be effected by one skilled in the art withoutdeparting from the spirit or scope of the invention as defined in theappended claims.

What is claimed is:
 1. A method of manufacturing an optical recordingmedium, comprising the steps of: separately fabricating a firstrecording member having a first light-transmissive substrate and a firstsemi-light-transmissive information area disposed on a surface of saidfirst light-transmissive substrate, and a second recording member havinga second substrate and a second reflective information area disposed ona surface of said second substrate; and joining said first recordingmember and said second recording member to each other with a transparentlayer interposed therebetween with the first and second informationareas facing each other.
 2. A method according to claim 1, wherein saidfirst and second light-transmissive substrates are respectively formedwith said first and second information areas by injection moldingprocesses.
 3. The method of claim 1, wherein said transparent layercomprises a photosetting transparent resin.
 4. A method of manufacturingan optical recording medium, comprising the steps of: fabricating afirst recording member comprising a first substrate having a firstinformation area and a second recording member comprising a secondsubstrate having a second information area by respectiveinjection-molding processes; forming a reflecting surface on said secondinformation area of said second substrate; and joining said firstrecording member and said second recording member to each other with atransparent layer interposed therebetween with the first and secondinformation areas facing each other.
 5. The method of claim 4, whereinsaid transparent layer comprises a photosetting transparent resin.
 6. Amethod of manufacturing an optical recording medium, comprising thesteps of: separately fabricating a first recording member having a firstlight-transmissive substrate and a first semi-light-transmissiveinformation area disposed on a surface of said first light-transmissivesubstrate, and a second recording member having a second substrate and asecond reflective information area disposed on a surface of said secondsubstrate; and joining said first recording member and said secondrecording member to each other with a transparent layer interposedtherebetween with the first and second information areas facing eachother, wherein said transparent layer is directly adhered to said firstand second information areas.
 7. A method of manufacturing an opticalrecording medium, comprising the steps of: separately fabricating afirst recording member having a first light-transmissive substrate and afirst semi-light-transmissive information area disposed on a surface ofsaid first light-transmissive substrate, and a second recording memberhaving a second substrate and a second reflective information areadisposed on a surface of said second substrate; and joining said firstrecording member and said second recording member to each other with atransparent layer interposed therebetween with the first and secondinformation areas facing each other, wherein said first information areahas a reflectance ranging from about 20% to about 50%, and atransmittance ranging from about 30% to about 80%, and said secondinformation area has a reflectance of about 60% or higher.
 8. A methodof manufacturing an optical recording medium, comprising the steps of:separately fabricating a first recording member having a firstlight-transmissive substrate and a first semi-light-transmissiveinformation area disposed on a surface of said first light-transmissivesubstrate, and a second recording member having a second substrate and asecond reflective information area disposed on a surface of said secondsubstrate; joining said first recording member and said second recordingmember to each other with a transparent layer interposed therebetweenwith the first and second information areas facing each other; andrecording information in said first and second information areas,whereby said information is progressively recorded in said firstinformation area as said optical recording medium is rotated in a firstdirection, and said information is progressively recorded in said firstinformation area as said optical recording medium is rotated in saidfirst direction.
 9. The method of claim 8, wherein said firstinformation area extends progressively radially outwardly, and saidsecond information area extends progressively radially inwardly as saidoptical recording medium is rotated in said first direction.
 10. Amethod of manufacturing an optical recording medium, comprising thesteps of: fabricating a first recording member comprising a firstsubstrate having a first information area and a second recording membercomprising a second substrate having a second information area byrespective injection-molding processes; forming a reflecting surface onsaid second information area of said second substrate; and joining saidfirst recording member and said second recording member to each otherwith a transparent layer interposed therebetween with the first andsecond information areas facing each other, wherein said transparentlayer is directly adhered to said first and second information areas.11. A method of manufacturing an optical recording medium, comprisingthe steps of: fabricating a first recording member comprising a firstsubstrate having a first information area and a second recording membercomprising a second substrate having a second information area byrespective injection-molding processes; forming a reflecting surface onsaid second information area of said second substrate; and joining saidfirst recording member and said second recording member to each otherwith a transparent layer interposed therebetween with the first andsecond information areas facing each other, wherein said firstinformation area has a reflectance ranging from about 20% to about 50%,and a transmittance ranging from about 30% to about 80%, and said secondinformation area has a reflectance of about 60% or higher.
 12. A methodof manufacturing an optical recording medium, comprising the steps of:fabricating a first recording member comprising a first substrate havinga first information area and a second recording member comprising asecond substrate having a second information area by respectiveinjection-molding processes; forming a reflecting surface on said secondinformation area of said second substrate; joining said first recordingmember and said second recording member to each other with a transparentlayer interposed therebetween with the first and second informationareas facing each other; and recording information in said first andsecond information areas, whereby said information is progressivelyrecorded in said first information area as said optical recording mediumis rotated in a first direction, and said information is progressivelyrecorded in said first information area as said optical recording mediumis rotated in said first direction.
 13. The method of claim 12, whereinsaid first information area extends progressively radially outwardly,and said second information area extends progressively radially inwardlyas said optical recording medium is rotated in said first direction.